The brain consists of a plurality of neurons that communicate with each other via chemical messengers. Each neuron generates neurochemicals or neurotransmitters which act at sites being referred to as receptors on the cellular membrane of neurons. One group of neurotransmitters, referred to as the monoamine neurotransmitters, includes serotonin, dopamine and noradrenaline.
Monoamine neurotransmitters are released into the synaptic cleft between neurons in order to stimulate postsynaptic receptor activity. The removal (or inactivation) of monoamine neurotransmitters occurs mainly by a reuptake mechanism into the presynaptic terminals. By inhibiting the re-uptake an enhancement of the physiological activity of monoamine neurotransmitters occur.
The serotonergic neural system of the brain have been shown to influence a variety of physiologic functions, and compounds having serotonin re-uptake inhibiting activity are predicted to have the ability to treat in mammals, including humans, a variety of disorders associated with this neural system, for example eating disorders, depression, obsessive compulsive disorders, panic disorders, alcoholism, pain, memory deficits and anxiety. Included among these disorders are disorders related to depression, such as pseudodementia or Ganser's syndrome, migraine pain, bulimia, obesity, pre-menstrual syndrome or late luteal phase syndrome, tobacco abuse, panic disorder, post-traumatic syndrome, memory loss, dementia of ageing, acquired immunodeficiency syndrome dementia complex, memory dysfunction in ageing, social phobia, attention deficit hyperactivity disorder, chronic fatigue syndrome, premature ejaculation, erectile difficulty, anorexia nervosa, disorders of sleep, autism, mutism or trichotillomania.
The pathophysiology of major affective illness is poorly understood, and several neurotransmitters have been implicated in the pathophysiology of major depression.
Mixed noradrenalin and serotonin re-uptake inhibitors, such as Imipramine and Amitriptyline and noradrenaline-reuptake inhibitors, such as Desipramine, Nortriptyline, and Protriptyline are currently used pharmaceuticals in anti-depressant therapy. Moreover, several lines of preclinical and clinical evidence indicate that an enhancement of serotonin-mediated neurotransmission might underlie the therapeutic effect of the most recent and currently used drugs in anti-depressant therapy: Fluoxetine, Citalopram and Paroxetine.
Paradoxical currently used serotonin re-uptake inhibitors inhibit the serotonin transporter within minutes whereas their full anti-depressant effect is seen only after three to four weeks of treatment, indicating that re-uptake inhibition per se is not responsible for the antidepressant response, but rather that further adaptive changes underlie and/or contribute to their therapeutic effect. The delayed onset of anti-depressant effect is considered to be a serious drawback to currently used monoamine re-uptake inhibitors.
A strong dopamine re-uptake inhibiting activity is considered with the risk of undesirable central stimulating effects. On the other hand, an activating effect on the mesolimbic dopamine system is believed to underlay the commen mechanism of current antidepressant treatment by a mechanism which enhances the endogenous reward system. Compounds with a strong serotonin re-uptake inhibiting activity combined with a well balanced moderate dopamine re-uptake inhibiting activity may therefore provide agents with a rapid onset of anti-depressant effect.
The compounds of the present invention are also valuable dopamine reuptake inhibitors and are as such considered useful for the treatment of Parkinsonism, depression, obesity, narcolepsy, drug addiction or misuse, including cocaine abuse, attention-deficit hyperactivity disorders, Gilles de la Tourettes disease and senile dementia. Dopamine re-uptake inhibitors enhances indirectly via the dopamine neurones the release of acetylcholin and are therefore also useful for the treatment of memory deficits, e.g. in Alzheimers disease, presenile dementia, memory dysfunction in ageing, and chronic fatigue syndrome. Noradrenaline re-uptake inhibitors are considered useful for enhancing attention, alertness, arousal, vigilance and for treating depression.